1. Field of the Invention
The invention relates to a magnetic recording and reproducing apparatus having a magnetic recording medium such as a discrete track medium and a patterned medium, a method of controlling the same, a magnetic recording medium, and a stamper for manufacturing a magnetic recording medium.
2. Description of the Related Art
Conventionally, a magnetic recording and reproducing apparatus that has a magnetic recording medium on which a positional information to be used for a positioning control of its magnetic head is recorded has been known widely.
FIG. 19 shows an example of the magnetic recording medium with which such conventional, publicly-known magnetic recording and reproducing apparatus is equipped.
The magnetic recording medium 100 shown in FIG. 19 has a plurality of servo regions 102 which are formed in radial shape at predetermined intervals, each formed of a concavo-convex pattern formed of a magnetic layer. As shown enlarged in FIG. 20, each of the servo regions 102 stores servo information which includes a preamble part 104, a servo mark part 106, an address part 108 which contains address information, and a burst part 110 which contains a positional information. The reference numeral 112 in the diagram designates data tracks for storing user data.
A burst pattern composed of four types of burst signal groups 110A, 110B, 110C, and 110D is formed in this burst part 110 of the servo region 102 as the positional information. The burst signal groups 110A and 110B are arranged to lie evenly across the center line of the data tracks 112 as a pair of pieces of the positional information. Meanwhile, the burst signal groups 110C and 110D are arranged to lie a half track pitch off from the burst signal groups 110A and 110B as another pair of pieces of the positional information.
FIG. 21 is an enlarged view of the burst signal group 110A. Incidentally, the other burst signal groups 110B, 110C, and 110D also have the same structure.
As shown in FIG. 21, the burst signal group 110A (110B, 110C, 110D) consists of a plurality (typically 10 to 30 or so) of convex portions (the crosshatched areas in FIG. 21) formed of a magnetic layer (magnetic material), the convex portions being arranged in the circumferential direction. The convex portions have a length of BL1 in the circumferential direction, and a width of BW1 in the radial direction and concave portions have a length of BL2 in the circumferential direction. In typical magnetic recording and reproducing apparatus, the magnetic recording medium 100 is rotated at a constant angular velocity. The circumferential length BL1 of the convex portions and the circumferential length BL2 of the concave portions thus depend on the radial position on the magnetic recording medium 100. The concavo-convex pattern is then formed so that the circumferential length BL1 of the convex portions and the circumferential length BL2 of the concave portions increase from the inner to the outer periphery.
The burst pattern of the burst part 110 is formed by arranging a plurality of individual burst signal groups (110A, 110B, 110C, 110D) in the radial direction at intervals of a width BW2 as shown in FIG. 22.
Such a burst pattern is reproduced, for example, by a position control circuit 130 shown in FIG. 23. This position control circuit 130 comprises an amplifier 116, a differentiator 118, a zero crossing detector 120, a comparator 122, a peak detector 124, a sample hold unit 126, and a differential amplifier circuit 128, and constitutes a circuit intended for a positioning control of so-called peak detected type. The amplifier 116 amplifies a reproduced signal read by a magnetic head 114. The differentiator differentiates the reproduced signal. The comparator 122 generates a predetermined gate pulse signal. The peak detector 124 detects a maximum output (peak output) of the reproduced signal and generates a position control signal. The sample hold unit 126 holds the position control signal.
The zero crossing detector 120 is a circuit for generating a predetermined signal while the signal differentiated by the differentiator 118 has zero intensity. For example, it generates the predetermined signal when the reproduced output read by the magnetic head 114 has a maximum value (peak value).
The comparator 122 is configured to generate a gate pulse when the reproduced output reaches or exceeds a certain output. Since the zero crossing detector 120 can generate the predetermined signal even if the reproduced output is zero, unnecessary signals occurring from the zero crossing detector 120 are removed by gate pulse signal.
After a burst pattern recorded on the magnetic recording medium 100 is read by the magnetic head 114, the signal reproduced from the burst pattern is amplified by the amplifier 116, and input to the differentiator 118. The reproduced signal differentiated by the differentiator 118 is passed through the zero crossing detector 120, and then input to the peak detector 124. Subsequently, the peak detector 124 detects a position where the gate pulse signal from the comparator 122 and the signal from the zero crossing detector 120 both are present. The reproduced output from the amplifier 116 at that position is the maximum output (peak output). This maximum output is output to the sample hold unit 126 as a position control signal. Then, the differential amplifier 128 determines a difference in output between the position control signal of the burst signal group 110A and the position control signal of the burst signal group 110B which are held in the sample hold unit 126, or a difference in output between the position control signal of the burst signal group 110C and the position control signal of the burst signal group 110D. The positional information on the magnetic head 114 is thus acquired, followed by a positioning (tracking) control of the magnetic head 114 (for example, see Japanese Patent Laid-Open Publication No. 2003-323772).
Now, in such magnetic recording media as a discrete track medium and a patterned medium, on which burst patterns (positional information) are recorded in the form of a concavo-convex pattern formed of a magnetic layer, magnetization signals of the concavo-convex pattern are recorded with one direction of polarity. Thus, signals reproduced from the concavo-convex pattern thus have a waveform like shown in FIG. 24. Incidentally, the crosshatched areas in FIG. 24 schematically show the plane of the convex portions of the concavo-convex pattern. The waveform of the signal reproduced from the concavo-convex pattern is for situations where the magnetic layer is a perpendicular magnetic recording layer.
As seen above, in magnetic recording media on which burst patterns are recorded in the form of a concavo-convex pattern formed of a magnetic layer, the position control signals to be used for the positioning control of the magnetic head fall to a half or so in output as compared to another example of conventional magnetic recording medium with continuous-film where magnetization signals of the burst patterns are recorded with two directions of polarity. Therefore, improvements on the positioning accuracy of the magnetic head have thus been limited.
Besides, the position control signals are highly susceptible to errors in the configuration, arrangement, and the like of the concavo-convex pattern. To obtain accurate position control signals requires that the concavo-convex pattern be formed with high accuracy, which has caused the problems of an increased manufacturing burden and manufacturing cost.